US patent application No. 20070233001 discloses an injection apparatus for delivering a pharmaceutical liquid to a patient. The injection apparatus comprises a needle cassette containing a plurality of drug injection needles; a drug cartridge containing a liquid and including a sealable aperture for accessing the liquid, a drive assembly engageable with the drug cartridge to expel the liquid through the aperture; a lifter assembly engageable with the needle cassette to drive one of the needles into a patient while simultaneously accessing the liquid in the drug cartridge through the aperture and thereafter to withdraw the needle from the patient after a measured dose of the liquid has been administered. The lifter assembly uses two springs. One spring acts to move the lifter downward to drive the needle into the patient at the start of an injection. The other spring acts to move the lifter upward to thereby withdraw the needle from the patient after a medicine injection is completed.
However, it is difficult to stably and precisely control movement of the needles using a lifter assembly which uses springs to drive the needles.
Hence there is a desire for an improved lifter assembly which can overcome the above mentioned problem.